Blood components, such as platelets, are typically stored for up to five or seven days before subsequent transfusion to a patient. Such platelets for storage are separated from whole blood. Although an apheresis system may be used, platelets may also be separated using a whole blood separator. In this process whole blood is collected from a donor and then subsequently (i.e., eight hours later), the collected whole blood is separated into a platelet product which may be called an interim platelet unit, or IPU. Such platelet product may not be sufficient for a full platelet medical or therapeutic dose. Thus each separated platelet component or IPU will be combined with other platelet products, (which could be from other donors), to form a transfusable dose.
In the past, platelet storage bags or containers for storage of either the IPU or the final platelet product have been made of a single material. Such bags or containers are typically made of polymers such as poly(vinyl chloride), (PVC) or poly-olefins such as SEBS (Styrene-Ethylene-Butylene-Styrene). The polymers are typically compounded with a plasticizer. The polymer material may be heat or high frequency welded together from two plastic sheets of the same material to form the bag. Alternatively, the bag may be blow molded.
Plasticizers compounded with PVC add transparency, flexibility, strength and stability at high and low temperatures to the base PVC polymer. The plasticizers also add permeability to water, oxygen, and carbon dioxide to the base PVC. Although there are a wide range of plasticizers currently available, the choice of plasticizer for blood or blood component contact applications, such as platelet contact applications, are more limited.
The most common plasticizer used for platelet storage containers is di, (2-ethyl hexyl)phthalate (DEHP). Although DEHP adds some permeability to the PVC, the resulting PVC/DEHP material needs to be of a thickness for the necessary carbon dioxide and oxygen permeability.
Another plasticizer suitable for compounding with PVC for blood component contact applications is tri octyl tri mellitate, (TOTM), although such plasticizer is not considered to add as much permeability as DEHP.
Citrate plasticizers have also been used with PVC as a storage bag composition. The use of n-butyrul, tri n-hyxyl citrate (BTHC) plasticizer has been shown to be effective for storing platelets. However, although BTHC plasticizer containers have sufficient oxygen permeability, the carbon dioxide permeability may be such that too much carbon dioxide escapes. Thus the permeability to carbon dioxide may be too great for optimum storage.
Embodiments of the present invention have been made in light of these and other considerations. However, the relatively specific problems discussed above do not limit the applicability of the embodiments of the present invention to solving other problems.